I'm also wary of free wifi spots since anyone can sniff non-encrypted traffic. Not a big deal to some, but it is to me.
I respect your concern and share the same thoughts myself. Here's my take on it. When on the net, we are all subject to having our activities monitored, recorded and stored, resold, you name it. There is no security, or very little. That's a fact that is very real.
So the way I deal with it is easy, I simply don't do anything on the net that I would not want to have to face at a later date. 3G is no more secure that a public open WiFi spot.
Furthermore neither is your secured Home WiFi network. While it's more secure than an open unsecured network, the fact is that anyone that wants to obtain your data and browsing habits can. It's just a fact.
Even encryption can be overcome. RSA is no longer as secure as it once was nor are other forms. Believe me I have a very good long time friend who is very high up in the FBI, he was a college buddy of mine at MIT and we are both working in the field of computers today.
Far too many people have a false sense of security and will go to great lengths to argue that there is privacy and safety.
Too bad that's a thing of the past.